Muscarinic Blocking Drugs: Absorption, Metabolism, and Excretion

ABSORPTION, METABOLISM, AND EXCRETION

Both atropine and scopolamine are tertiary amines that cross biological membranes readily. They are well ab-sorbed from the gastrointestinal tract and conjunctiva and can cross the blood-brain barrier. After the intra-venous injection of atropine (DL-hyoscyamine), the bio-logically inactive isomer, D-hyoscyamine, is excreted un-changed in the urine. The active isomer, however, can undergo dealkylation, oxidation, and hydrolysis.

The quaternary ammonium derivatives of the bel-ladonna alkaloids, as well as the synthetic quaternary ammonium compounds, are incompletely absorbed from the gastrointestinal tract. Consequently, greater amounts of these compounds are eliminated in the feces following oral administration. The blood-brain barrier prevents quaternary ammonium muscarinic blockers from gaining significant access to the CNS.